1. Field of the Invention
This invention relates to an integrated optoelectronic device for constructing electronic equipment, and an integrated circuit device, and particularly to (i) an integrated optoelectronic device, wherein optical and electronic devices are integrated to transmit or receive signals via light or a mixture of electrical means and light, such as optical interconnections, (ii) its driving method, (iii) a method of wiring between a mixed optoelectronic substrate and the integrated optoelectronic device, and (iv) related structures.
2. Related Background Art
In recent years, the development of high-speed large scale integration (LSI) has been advanced as the speeds of computers, information processing and computer peripherals, such as displays and printers, have increased. At the same time, problems of signal delay, heat generation and electromagnetic radiation emission noise (EMI) due to the rapid switching rates of the circuits in the LSI chip, integrated circuit (IC) board, multi-chip-module (MCM), and the backplane of super computers, and connections between electronic devices such as boards, computers, peripheral equipment, and audio-visual (AV) apparatuses have proliferated. Solutions of those problems are, however, difficult. It is hence apparent that the inherent absolute physical limitations of electric wiring will be reached in the near future.
For the purposes of solving the problems in the electrical wiring, there has been developed a substrate using a micro strip-line of the Rambus system in a board, or a method of transmitting a low voltage differential signal with a small amplitude through a shield line between boards (low voltage differential signalling (LVDS)).
In the Rambus system, signal transmission of frequencies over 400 MHz has been achieved, and this system is planned to be introduced in a next generation personal computer (PC). There are, however, limitations to the manner of wiring, and the implementation and arrangement of pins on the side of LSI chips. Therefore, there are problems in that system in that the chip cost increases, the system is unsuitable for long wiring, and the size of the board increases due to the limitations as to a high density in multi-bit wiring since cross-talk must be eliminated.
In the LVDS method, high-speed serial transmission of about 1 Gbps using LVDS has been put into practice, but its range of use is restricted since the costs of its interface IC and cable are high.
As a potential method for solving the limitations inherent in electrical wiring, techniques of optical interconnections are under development. In an optical interconnection, an electric signal from the IC or the like is converted into an optical signal, the converted optical signal is transmitted through an optical channel, or xe2x80x9cwiringxe2x80x9d, as used hereinbelow, such as a waveguide formed in a board, to an optical receiver in another IC or board, and the optical signal is reconverted into an electric signal. Such a system removes the problem of (i) signal delay due to the parasitic capacitance that appears in electric wiring, (ii) signal degradation resulting from an unstable ground, and (iii) emission of EMI radiating from the wiring, and the system is thus expected to be used in future wiring schemes. In the optical interconnection, portions of the O (optical)/E (electrical) and E (electrical)/O (optical) conversions and the waveguide are important, and therefore, it is critical how effectively a portion of the electric wiring can be replaced by the optical wiring at a reduced cost.
As a method of optical wiring, there exists, as disclosed in Japanese Patent Application Laid-Open No. 5(1993)-67770, a structure wherein an optoelectronic IC chip, with an optical device arranged in place of the pins of the IC chip, is implemented on an optical wiring substrate provided with a waveguide and a reflective mirror. FIG. 1 illustrates the structure. A light emitting device 1011 is provided on the bottom surface of an optoelectric IC chip 1004, an inclined portion 1005 acting as a reflective mirror is provided on an optical wiring substrate 1001, and an optical signal from the light emitting device 1011 is coupled to a waveguide (core) 1008 and then received by a light receiving device 1012 in another chip 1004. In this example, a manner of the optical coupling between the optical devices 1011 and 1012 and the waveguide 1008 is illustrated, but neither the specific integration method nor the driving method of the electric circuit portion 1010 or the optical devices 1011 and 1012 is described. There is further provided in the structure of FIG. 1 a reflective layer 1002, a protruded portion 1006, and a silicon-oxide layer 1007.
As a method of driving an optical device to achieve the optical wiring, the following method is disclosed in Japanese Patent Application Laid-Open No. 9(1997)-96746. As illustrated in FIG. 2A, a continuous-wave output from a laser diode 1101 is divided by a coupler formed of plane waveguides into portions whose number is the number of signal lines, and electric signals are converted to optical signals by optical modulators 1102 of the electric-field absorption type or optical switches of a Mach-Zehnder type, respectively. Each optical signal is received and converted to an electric signal by a photodetector (PD) 1103, and the electric signal is amplified by an amplifier 1104. In this case, the substrate is not complicated and there is no need to prepare a special IC for driving the optical device, since the electric wiring portion 1106 and the optical wiring portion 1105 in the transmitter are independently designed as illustrated in FIG. 2B and an electric wiring portion 1107 and an optical wiring portion in the receiver portion are independently designed as illustrated in FIG. 2C. This construction can be readily applied to any electronic equipment simply by placing the optical wiring portion on a conventional electric printed circuit board (PCB), or the like.
In the system depicted in FIGS. 2A to 2C, however, the thickness of the structure increases due to the optical wiring portion being provided separately from the electric circuit, as described above. Accordingly, the size is inevitably made larger, as compared with the mixed optoelectronic substrate of FIG. 1. Further, in the case of a multi-channel device, or plurality of high-performance devices, such as an optical modulator or an optical switch, the cost increases, and problems arise with respect to the reliability of the electrode contacts of the electric signal to the modulator, to implementation, and to cross-talk between the modulators. Furthermore, the optical loss is large since light is divided by the coupler and coupled to the optical modulator, or the like, and hence, the problem arises of the electric power required to sustain the output power of the laser.
In the system of FIG. 1, although the detailed device construction and method of implementation are not clearly shown, it seems that the optical device and the electric device are commonly packaged, that the size is decreased due to high-density integration, and that reliability of the wiring is improved. This system is, however, impractical because of the power required to drive an ordinary light emitting device (due to the large electrical currents involved), such as a light emitting diode (LED) or a semiconductor laser. Additionally, the integrated circuit is further complicated by the addition of an IC for driving the optical device.
It is an object of the present invention to provide a practical integrated optoelectronic device which is readily adaptable to an optical interconnection and whose electric power requirements, as well as cost, can be reduced, an integrated circuit device, and related structures and methods.
The present invention is generally directed to an integrated optoelectronic device which includes an electric circuit unit, such as a bare chip of integrated electronic devices, and an optical device unit for performing at least a portion of the signal input and output to and from the electric circuit unit via an optical signal. The electric circuit unit and the optical device unit are packaged in a common package having contoured upper, lower, and side surfaces, and the optical device unit is placed on the side surface of the package. In such a structure, the electric circuit unit, such as an LSI circuit, and the optical device unit for performing an O/E or E/O conversion, are commonly packaged, so that the optical wiring and the electric wiring can be arranged in a compact manner, with low power requirements and at a reduced cost. Furthermore, the length of the wiring can be shortened, and hence, signal delay and skew can be prevented.
The following more specific structures are possible in the above structure.
The optical device unit is optically coupled to an external waveguide at the side surface of the package. The optical device unit may comprise a surface light emitting device unit, such as a surface emitting laser. In this case, the arrangement of devices and wiring in the package can be facilitated, and the arraying of the optical devices can be readily attained. Further, when the integrated optoelectronic device is implemented on a plate having both an electric wiring substrate and a waveguide layer formed thereon, the light input/output surface of the optical device can be readily and accurately aligned with the end surface of the waveguide.
The optical coupling is conducted horizontally with respect to the integrated optoelectronic device. The integrated optoelectronic device can be constructed in such a manner so as to establish an electrical contact with an external electric wiring substrate at the lower surface of the package.
The integrated optoelectronic device may further comprise a driving circuit for controlling the unit of the optical device, as well as wiring means for electrically connecting the driving circuit to the optical device unit, and the driving circuit and the wiring means may also be packaged in the common package.
The package may include a base plate, and the electric circuit unit and the optical device unit may be fixed on the base plate in proximity to each other with the wiring means interposed therebetween. In this structure, the electric circuit unit will thus be fixed on a central portion of the base plate, and the optical device unit will be fixed on the peripheral portion of the base plate in proximity to the electric circuit unit with the wiring means interposed therebetween. In this case, the optical device unit may be fixed in such a manner that an input or an output of light in or from the optical device is performed in a direction, or plane, parallel to the base plate. Further, an exposed conductive portion for electrically connecting to an external electric wiring may be provided in a region between the optical device unit and the electric circuit unit.
Further, the optical device unit may include optical devices arranged in an array on a wiring substrate with separate electrodes of the optical devices being bonded to the wiring substrate in a flip-chip manner, the wiring substrate may be fixed to a structure commonly packaged with the electric circuit unit, and windows for transmitting light may be formed in the wiring substrate or in the structure, corresponding to the arrayed optical devices.
The arrayed optical devices may, for example, be surface emitting lasers sandwiched between the structure and the wiring substrate, and the surface emitting laser may have a structure in which its growth semiconductor substrate is removed with only its cavity layer, including a multi-layer reflective mirror and an active layer, remaining.
The type of the package may be a ball grid array (BGA) in which the electric circuit unit is bonded to a base plate and an array of solder balls is arranged on a structure bonded to a portion of the base plate around the electric circuit unit, and the optical device may be bonded to a side surface of the structure such that an input or an output of light to or from the optical device is performed at the side surface of the package.
The optical device may be a surface emitting laser, such surface emitting laser may be driven directly by the on-and-off switching of a CMOS buffer at an output stage of the driving circuit, and the driving current of the surface emitting laser may be controlled by a resistor inserted in the signal path in series with the surface emitting laser.
Further, the present invention is generally directed to an integrated circuit device which includes an integrated optoelectronic device including an electrode region formed on a central portion of its bottom surface and an optical device region formed around the electrode region, and a plate member including an electric wiring substrate with an optical wiring layer provided on the electric wiring substrate. The electrode region has a protruding configuration, the plate member has a recess, and the protruding configuration has a height corresponding to the thickness of the optical wiring layer, and is inserted in the recess.
The optical wiring layer may be provided on each of upper and lower surfaces of the electric wiring substrate, and the integrated optoelectronic device may be placed on each of the optical wiring layers.
The electric wiring substrate may have a through-hole waveguide for optically coupling the optical wiring layers to each other.
These advantages and others will be more readily understood in connection with the following detailed description of the more preferred embodiments in conjunction with the drawings.